linux-kernel - Re: [PATCH 02/14] soundwire: Add SoundWire bus type

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Date:   Fri, 20 Oct 2017 08:59:42 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        ALSA <alsa-devel@...a-project.org>, Mark <broonie@...nel.org>,
        Pierre <pierre-louis.bossart@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        Shreyas NC <shreyas.nc@...el.com>, patches.audio@...el.com,
        alan@...ux.intel.com,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Sagar Dharia <sdharia@...eaurora.org>,
        srinivas.kandagatla@...aro.org, plai@...eaurora.org,
        Sudheer Papothi <spapothi@...eaurora.org>
Subject: Re: [PATCH 02/14] soundwire: Add SoundWire bus type

On Fri, 20 Oct 2017 07:11:01 +0200,
Vinod Koul wrote:
> 
> On Thu, Oct 19, 2017 at 09:40:06AM +0200, Takashi Iwai wrote:
> > On Thu, 19 Oct 2017 05:03:18 +0200,
> > Vinod Koul wrote:
> > > +
> > > +config SOUNDWIRE_BUS
> > > +	tristate
> > > +	default SOUNDWIRE
> > > +
> > 
> > Does it make sense to be tristate?
> > Since CONFIG_SOUNDWIRE is a bool, the above would be also only either
> > Y or N.  If it's Y and others select M, it'll be still Y.
> 
> hmmm good point. I think would make sense to make SOUNDWIRE as tristate too,
> just like SOUND :)

It's one option.  Another would be to simply drop the "default" line.

> > > + * The match is done by comparing the mfg_id and part_id from the
> > > + * struct sdw_device_id. class_id is unused, as it is a placeholder
> > > + * in MIPI Spec.
> > > + */
> > > +static const struct sdw_device_id *
> > > +sdw_get_device_id(struct sdw_slave *slave, struct sdw_driver *drv)
> > > +{
> > > +	const struct sdw_device_id *id = drv->id_table;
> > > +
> > > +	while (id && id->mfg_id) {
> > > +		if (slave->id.mfg_id == id->mfg_id &&
> > > +				slave->id.part_id == id->part_id) {
> > 
> > Please indentation properly.
> 
> what do you advise?
> 
> 		if (slave->id.mfg_id == id->mfg_id &&
> 			slave->id.part_id == id->part_id) {
> 
> would mean below one is at same indent. Some people use:
> 
> 		if (slave->id.mfg_id == id->mfg_id &&
> 		   slave->id.part_id == id->part_id) {
> 
> Is it Documented anywhere...

This is a matter of taste.  The latter is the way Emacs or indent does
as default.

> > > --- a/include/linux/mod_devicetable.h
> > > +++ b/include/linux/mod_devicetable.h
> > > @@ -228,6 +228,13 @@ struct hda_device_id {
> > >  	unsigned long driver_data;
> > >  };
> > >  
> > > +struct sdw_device_id {
> > > +	__u16 mfg_id;
> > > +	__u16 part_id;
> > > +	__u8 class_id;
> > > +	kernel_ulong_t driver_data;
> > 
> > Better to think of alignment.
> 
> sorry not quite clear, do you mind elaborating which ones to align?

kernel_ulong_t may be aligned to 4 or 8 bytes, depending on
architecture, so there can be a hole between class_id and driver_data.
It's not an ABI, so we don't have to care too much, but it's still
something exposed, hence better to be conscious about alignment.


Takashi